import { saveAs } from 'file-saver'
import XLSX from 'xlsx'

function datenum(v, date1904) {
  if (date1904) v += 1462
  const epoch = Date.parse(v)
  return (epoch - new Date(Date.UTC(1899, 11, 30))) / (24 * 60 * 60 * 1000)
}

function sheet_from_array_of_arrays(data) {
  const ws = {}
  const range = { s: { c: 10000000, r: 10000000 }, e: { c: 0, r: 0 } }
  for (let R = 0; R !== data.length; ++R) {
    for (let C = 0; C !== data[R].length; ++C) {
      if (range.s.r > R) range.s.r = R
      if (range.s.c > C) range.s.c = C
      if (range.e.r < R) range.e.r = R
      if (range.e.c < C) range.e.c = C

      const cell = { v: data[R][C] }
      if (cell.v == null) continue
      const cell_ref = XLSX.utils.encode_cell({ c: C, r: R })

      if (typeof cell.v === 'number') cell.t = 'n'
      else if (typeof cell.v === 'boolean') cell.t = 'b'
      else if (cell.v instanceof Date) {
        cell.t = 'n'
        cell.z = XLSX.SSF._table[14]
        cell.v = datenum(cell.v)
      } else cell.t = 's'

      ws[cell_ref] = cell
    }
  }
  if (range.s.c < 10000000) ws['!ref'] = XLSX.utils.encode_range(range)
  return ws
}

function Workbook() {
  if (!(this instanceof Workbook)) return new Workbook()
  this.SheetNames = []
  this.Sheets = {}
}

function s2ab(s) {
  const buf = new ArrayBuffer(s.length)
  const view = new Uint8Array(buf)
  for (let i = 0; i !== s.length; ++i) view[i] = s.charCodeAt(i) & 0xff
  return buf
}

export function export_json_to_excel({ multiHeader = [], header, data, filename, merges = [], autoWidth = true, bookType = 'xlsx' } = {}) {
  // original data
  filename = filename || 'excel-list'
  data = [...data]
  data.unshift(header)

  for (let i = multiHeader.length - 1; i > -1; i--) {
    data.unshift(multiHeader[i])
  }

  const ws_name = 'SheetJS'
  const wb = new Workbook()
  const ws = sheet_from_array_of_arrays(data)

  if (merges.length > 0) {
    if (!ws['!merges']) ws['!merges'] = []
    merges.forEach(item => ws['!merges'].push(XLSX.utils.decode_range(item)))
  }

  if (autoWidth) {
    // 设置worksheet每列的最大宽度
    const colWidth = data.map(row =>
      row.map(val => {
        // 先判断是否为null/undefined
        if (val == null) return { wch: 10 }
        // 再判断是否为中文
        else if (val.toString().charCodeAt(0) > 255) return { wch: val.toString().length * 2 }
        else return { wch: val.toString().length }
      })
    )
    // 以第一行为初始值
    const result = colWidth[0]
    for (let i = 1; i < colWidth.length; i++) {
      for (let j = 0; j < colWidth[i].length; j++) {
        if (result[j]['wch'] < colWidth[i][j]['wch']) {
          result[j]['wch'] = colWidth[i][j]['wch']
        }
      }
    }
    ws['!cols'] = result
  }

  // add worksheet to workbook
  wb.SheetNames.push(ws_name)
  wb.Sheets[ws_name] = ws

  const wbout = XLSX.write(wb, { bookType: bookType, bookSST: false, type: 'binary' })
  saveAs(new Blob([s2ab(wbout)], { type: 'application/octet-stream' }), `${filename}.${bookType}`)
}
